1. Field of the Invention
The present invention pertains to airfoil structures of composite material used in part of an aircraft elevator or wing, for example, as well as to methods of forming such airfoil structures. More particularly, the invention relates to airfoil structures of composite material which are easy to manufacture and provide a high peeling strength as well as to their forming methods.
2. Description of the Related Art
FIGS. 19 to 21 show an elevator surface structure of a related art aircraft using composite materials, in which the aircraft""s elevator I is constructed by individually forming an upper skin 2, a lower skin 3, a spar 4 and ribs 5 using the composite materials and, then, assembling them by use of fastener means 6, such as bolts and nuts.
The related art aircraft elevator 1 has such problems that it involves a large number of principal constituent components, requiring high manufacturing costs for those components, and because they need to be assembled by using a number of fasteners, assembling component costs are also high. A further problem is that it is necessary to make many holes for fitting the fasteners, resulting in an increase in man-hours required for assembly work.
Box-structure airfoils in which a frame is produced by previously fastening spars and ribs with clips to reduce the man-hours required for assembly with fasteners and upper and lower skins bonded to the frame are disclosed in European Patent Bulletin Publication No. 485027 and published U.S. Pat. No. 5,216,799, for example.
Although it has been attempted to reduce the number of fasteners and the man-hours required for assembly by assembling the individual skins by bonding in the aforementioned box-structure airfoil, the number of components is not actually reduced because the principal components have the same construction as those of the related art. Further, as it is necessary to previously join the spars and ribs with fasteners and then adjust mating surfaces by machining flange surfaces of the spars and ribs after frame assembly, there arises a problem that man-hour requirements are increased.
Also, structures shown in FIGS. 22 and 23 in which a frame 7 and a skin 8 are bonded by using an adhesive 9 have a low out-of-plane peeling load (peeling load exerted in a direction perpendicular to the skin 8) compared to fastener assembly, and this would pose a problem related to strength.
Although it is advantageous for improving the peeling strength if the frame 7 has an I-shaped cross section rather than a U-shaped cross section, the frame 7 of the I-shaped cross section entails approximately twice as high manufacturing cost as the frame 7 of the U-shaped cross section, thus developing a problem of increased cost.
The invention has been made in consideration of these situations. Accordingly, it is an object of the invention to provide airfoil structures of composite material which make it possible to reduce the number of principal constituent components and assembling components to thereby achieve cost reduction, as well as methods of forming such airfoil structures.
A composite material airfoil structure of the invention comprises a composite material skin which forms one of top and bottom surfaces of an airfoil, a second composite material skin which forms the other of the top and bottom surfaces of the airfoil, a composite material spar having flanges and a web which together form a U-shaped cross section, the spar being attached to at least one terminal portion of the skins, composite material ribs and an elongate projection for adhesive bonding of the spar, the ribs and elongate projection being located between the skins, wherein the ribs and elongate projection are formed integrally with at least one of the skins In this airfoil structure, it becomes possible to reduce the number of principal constituent components and thereby achieve cost reduction. Furthermore, by bonding the individual flanges of the spar to individual skin members, it becomes possible to obtain a peeling strength equivalent to that achieved when using a spar having an I-shaped cross section even when the spar having the U-shaped cross section is used to achieve cost reduction.
In a composite material airfoil structure of the invention, the ribs and elongate projection are formed integrally with one skin and their extreme ends are bonded to the other skin. In this airfoil structure, the construction of the skin having no ribs or elongate projection is simplified and it becomes possible to reduce manufacturing costs.
In a composite material airfoil structure of the invention, the ribs and elongate projection are formed integrally with each skin and their extreme ends are bonded to one another. In this airfoil structure, dimensions of the ribs and elongate projection rising out of each skin are reduced and it becomes possible to improve the overall strength of each skin one-piece formed with the ribs and elongate projection.
A method of forming a composite material airfoil structure of the invention comprises a molding process in which a first composite material skin which forms one surface of an airfoil and a second composite material skin which has ribs and an elongate projection integrally formed on an inner surface and forms the other surface of the airfoil are separately formed, and a bonding process in which bonding between extreme ends of the ribs and elongate projection and the first skin, bonding between individual flanges of a spar and the individual skins, and bonding between a web of the spar and the elongate projection are simultaneously done by using an adhesive to thereby form a single structure. This method makes it possible to reduce the number of principal constituent components and thereby achieve cost reduction. It also becomes possible to reduce the manufacturing costs as it is not necessary to use fasteners, for instance.
In a method of forming a composite material airfoil structure, the first skin is formed by laminating composite material prepreg on a mold base having the same outer contours as the airfoil, placing a foam core covered with a glue film on an upper surface of the prepreg, laminating again composite material prepreg on top, and hardening an entire assembly by thermosetting operation. Since this method uses the foam core as core material, pressures are uniformly allocated during a hardening process unlike the case in which an anisotropic core material like a honeycomb panel is used. Thus, it becomes possible to reduce deformation during the thermosetting operation.
In a method of forming a composite material airfoil structure, the second skin is formed by laminating composite material prepreg on a mold base having the same outer contours as the airfoil, placing a foam core covered with a glue film on the upper surface of the prepreg, laminating again composite material prepreg on top, placing an intra-projection foam core covered with a glue film on top, laminating again composite material prepreg on top, placing intra-rib foam cores covered with a glue film on top, laminating yet again composite material prepreg on top, and then hardening an entire assembly by thermosetting operation. Since this method uses the foam cores as core material, deformation is reduced even when the second skin and the ribs and elongate projection are one-piece molded. It also becomes possible to reduce the number of principal constituent components by one-piece molding the second skin with the ribs and elongate projection.
A method of forming a composite material airfoil structure of the invention comprises a molding process in which a first composite material skin which forms one surface of an airfoil and a second composite material skin which has ribs and an elongate projection integrally formed on an inner surface and forms the other surface of the airfoil are separately formed, and a bonding process in which bonding between extreme ends of ribs and elongate projections of the individual skins, bonding between individual flanges of a spar and the individual skins, and bonding between a web of the spar and the elongate projections are simultaneously done by using an adhesive to thereby form a single structure. This method makes it possible to reduce the number of principal constituent components and thereby achieve cost reduction. It also becomes possible to reduce the manufacturing costs as it is not necessary to use fasteners, for instance. Furthermore, since the ribs and elongate projection are integrally formed in halves on each skin, their dimensions rising out of each skin are reduced and it becomes possible to improve the overall strength of each skin one-piece formed with the ribs and elongate projection.
In a method of forming a composite material airfoil structure, each of the first and second skins is formed by laminating composite material prepreg on a mold base having the same outer contours as the airfoil, placing a foam core covered with a glue film on the upper surface of the prepreg, laminating again composite material prepreg on top, placing an intra-projection foam core covered with a glue film on top, laminating again composite material prepreg on top, placing intra-rib foam cores covered with a glue film on top, laminating yet again composite material prepreg on top, and then hardening an entire assembly by thermosetting operation. Since this method uses the foam cores as core material, it becomes possible to reduce deformation during the thermosetting operation even when the ribs and elongate projection are one-piece molded with each skin member.
In a method of forming a composite material airfoil structure, pressure plates are placed at least on end surfaces of the ribs and elongate projection prior to the thermosetting operation, the pressure plates having shapes corresponding to the shapes of mating bond surfaces. This arrangement eliminates the need to adjust the mating surfaces one by one when bonding the two skins to each other and makes it possible to simplify mismatch correction.
In a method of forming a composite material airfoil structure, a pasty thermosetting adhesive is used as the adhesive. As a consequence, a gap, whichever created between bond surfaces, is filled with the adhesive as long as the gap is about 2 mm wide or less, and it becomes possible to prevent a reduction in strength almost completely.